JP5681766B2 - Phosphorescent compound and organic light-emitting diode device using the same - Google Patents

Description

  The present invention relates to a phosphorescent compound used in an organic light-emitting diode device, and more particularly, a phosphorescent compound having a high triplet energy and a wide energy band gap and capable of improving luminous efficiency, and an organic light-emitting diode using the phosphorescent compound It relates to an element.

  Recently, with the increase in the size of display devices, the demand for flat display elements that occupy less space is increasing. As one of such flat display elements, an organic electroluminescent device (OELD) is also known. The technology related to the light emitting diode device has been developed at a high speed, and many trial products have already been announced.

  An organic light emitting diode element emits light while electrons and holes are paired and disappeared when a charge is injected into a light emitting material layer formed between an electron injection electrode (cathode) and a hole injection electrode (anode). It is an element. Not only can the element be formed on a flexible transparent substrate such as plastic, but it can be driven at a lower voltage (10 V or less) than a plasma display panel or an inorganic electroluminescent (EL) display. It has the advantages of low power consumption and excellent color purity. In addition, since organic electroluminescence (EL) elements can represent three colors of green, blue, and red, they are attracting attention as next-generation display elements having abundant colors. Here, the manufacturing process of the organic light emitting diode will be briefly described.

  (1) First, a material such as indium-tin-oxide (indium tin oxide: ITO) is deposited on a transparent substrate to form an anode.

  (2) A hole injecting layer (HIL) is formed on the anode. The hole injection layer is composed mainly of 4,4′-bis [N- [4- {N, N-bis (3-methylphenyl) amino} phenyl] -N— represented by the following chemical formula (1-1). Phenylamino] biphenyl (DNTPD) is formed by vapor deposition with a thickness of 10 nm to 60 nm.

  (3) Next, a hole transport layer (HTL) is formed on the hole injection layer. For the hole transport layer, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] -biphenyl (NPB) represented by the following chemical formula (1-2) is deposited by about 30 to 60 nm. Formed.

  (4) Next, an emissive material layer (EML) is formed on the hole transport layer. If necessary, dopants may be added to form red, green, and blue light emitting material layers for color realization. For example, the phosphorescent blue dopant tris ((3,5-difluoro) represented by the following chemical formula (1-4) is added to the host bis (N-carbazolyl) biphenyl (CBP) represented by the following chemical formula (1-3). -4-Cyanophenyl) pyridine) yldium (III) (FCNIr) is doped to form a blue luminescent material layer.

  (5) Subsequently, an electron transport layer (ETL: electron transport layer) and an electron injection layer (EIL: electron injection layer) are continuously formed on the light emitting material layer.

  (6) Next, a cathode is formed on the electron injection layer, and finally a protective film is formed on the cathode.

  Recently, a phosphorescent material is used more frequently in a light emitting material layer than a fluorescent material. The reason for this is that in the case of a fluorescent material, only about 25% of singlet excitons formed in the luminescent material layer are used for photogeneration, and 75% of triplets are mostly lost by heat, but phosphorescence. This is because the substance has a light emitting mechanism in which both singlet and triplet are converted into light. A phosphorescent dopant generally contains a heavy element such as Ir, Pt, or Eu at the center of an organic substance, and has a high electron transition probability from a triplet to a singlet.

  However, since such a dopant causes a sudden decrease in efficiency due to the concentration quenching phenomenon, a luminescent material layer cannot be formed alone. Therefore, the light emitting layer is formed together with a host having higher thermal stability and triplet energy than the dopant.

  Briefly explaining the light emitting process of an organic light emitting diode device containing a phosphor, a hole injected from the anode and an electron injected from the cathode meet at the host of the light emitting layer, and the singlet exciton formed by the host is a dopant. Energy transition to singlet or triplet occurs, and triplet excitons undergo energy transition to the triplet of the dopant. Since the exciton that has transitioned to the singlet of the dopant also transitions to the triplet of the dopant, the primary termination of all excitons becomes the triplet level of the dopant. The exciton thus formed transitions to the ground state and emits light.

  For efficient energy transfer to the dopant, the host triplet energy must be higher than the dopant triplet energy. When the triplet energy of the host is lower than the triplet energy of the dopant, an energy reverse transition from the dopant to the host occurs, and the efficiency decreases.

  That is, referring to FIG. 1, in the case of CBP that has been conventionally used as a host material, the triplet energy is 2.6 eV, HOMO (high occupied molecular orbital): -6.3 eV, LUMO (lowest unoccupied molecular orbital). : -2.8 eV, so when using FCNIr phosphorescent dopant (HOMO: -5.8 eV, LUMO: -3.0 eV, triplet energy: 2.8 eV), which is a blue phosphorescent dopant, the dopant to the host An energy reverse transition occurs and the efficiency decreases. In particular, a significant decrease in efficiency occurs at low temperatures.

  An object of the present invention is to provide a new phosphor having a triplet energy of 2.8 eV or more, excellent thermal stability, and a wide singlet energy gap of 3.3 eV or more, and preventing a decrease in luminous efficiency. And

  In particular, an object is to prevent a decrease in luminous efficiency by making the triplet energy of the host material higher than the triplet energy of the dopant.

  In order to solve the above-described problems, the present invention is represented by the following chemical formula, wherein each of X and Y is independently a group consisting of an aromatic compound and a heterocyclic compound. A phosphorescent compound selected from:

  In the phosphorescent compound of the present invention, each of the X and the Y is selected from the group consisting of carbazole, α-carboline, β-carboline, γ-carboline, pyridine, phenyl, dibenzofuran, and their substitutes. Features.

  In another aspect, the present invention includes: a first electrode; a second electrode facing the first electrode; and a luminescent material layer positioned between the first electrode and the second electrode, wherein the luminescent material layer Is represented by the following chemical formula, wherein each of X and Y independently comprises a phosphorescent compound selected from the group consisting of an aromatic compound and a heterocyclic compound: An element is provided.

  In the organic light-emitting diode device of the present invention, each of the X and the Y is selected from the group consisting of carbazole, α-carboline, β-carboline, γ-carboline, pyridine, phenyl, dibenzofuran, and their substituted products. It is characterized by that.

  In the organic light emitting diode device of the present invention, a hole injection layer located between the first electrode and the light emitting material layer, a hole transport layer located between the light emitting material layer and the hole injection layer, And an electron injecting layer positioned between the second electrode and the light emitting material layer, and an electron transporting layer positioned between the light emitting material layer and the electron injecting layer.

  Since the phosphor of the present invention has a triplet energy of 2.8 eV or more and a wide energy band gap of 3.3 eV or more, the efficiency of the organic light emitting diode device can be improved.

  In particular, the phosphor of the present invention can be used as a blue host in a light-emitting material layer and has a triplet energy higher than that of a dopant.

It is the PL spectrum of CBP which is a host material for the conventional organic light emitting diode element. 2 is a PL spectrum of a phosphor for an organic light emitting diode device according to an example of the present invention. 2 is a UV spectrum and a PL spectrum of a phosphor for an organic light emitting diode device according to an example of the present invention. 4 is a graph showing current density of a phosphor according to an example of the present invention. 3 is a graph showing current efficiency of a phosphor according to an example of the present invention. 4 is a graph illustrating power efficiency of a phosphor according to an embodiment of the present invention. 1 is a schematic cross-sectional view of an organic light emitting diode device according to an embodiment of the present invention.

  Hereinafter, the structure of the phosphorescent compound according to the present invention, a synthesis example thereof, and an organic light emitting diode device using the same will be described.

  The phosphorescent compound of the present invention is represented by the following chemical formula (2). That is, it has a structure in which aromatic compounds or heterocyclic compounds are substituted symmetrically or asymmetrically at positions 2 and 6 of pyridine, and has a high triplet energy and a wide energy band gap.

  In the chemical formula (2), each of X and Y is independently selected from an aromatic compound or a heterocyclic compound. X and Y may be the same or different.

  For example, each of X and Y is selected from unsubstituted carbazole represented by the following chemical formula (3), α-carboline, β-carboline, γ-carboline, pyridine, phenyl, dibenzofuran, or a substituted product thereof. Can.

  Further, the substitution product of X and Y may be carbazole, α-carboline, β-carboline, γ-carboline, dibenzofuran.

  In particular, the phosphorescent compound of the present invention has carbazole having strong triplet energy and carboline having high triplet energy at positions 2 and 6 of a pyridine core having strong electron characteristics. Substituting each asymmetrically improves the charge balancing of the holes and electrons and has an energy gap and high triplet energy compatible with the targeted blue dopant.

  For example, the substance of the chemical formula (2) is any one of a plurality of substances represented by the following chemical formula (4).

  Since the phosphorescent compound represented by the chemical formula (2) has a high triplet energy and a wide energy band gap as described below, the light emission efficiency is improved.

  Hereinafter, among the phosphorescent compounds according to the present invention, synthesis examples of phosphorescent compounds represented by the new host 1 and the new host 2 in the chemical formula (4) will be described.

  1. Synthesis of new host 1

  (1) Synthesis of 2,6-diiodopyridine

  2,6-Diiodopyridine was synthesized according to the following reaction formula (1).

  In a 250 mL 2-neck flask, 2,6-dibromopyridine (20.2 g, 84.427 mmol), copper iodide (3.86 g, 20.263 mmol), sodium iodide (50.62 g, 33 .708 mmol) and 1,2-dicyclohexanedimethyldiamine (5.86 mL, 37.148 mmol) were added and dissolved in 1,4-dioxane, followed by refluxing and stirring for 12 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure, column purification (hexane: methylene chloride = 3: 1) was performed, the purified solution was distilled under reduced pressure and recrystallized with methylene chloride / petroleum ether solvent, 9.88 g of a white solid was obtained (yield: 35%).

  (2) Synthesis of 9- (6-iodopyridin-2-yl) -9H-pyrido [2,3-b] indole

  9- (6-Iodopyridin-2-yl) -9H-pyrido [2,3-b] indole was synthesized according to the following reaction formula (2).

  In a 250 mL two-necked flask, 2,6-diiodopyridine (4.13 g, 12.486 mmol), carboline (1.0 g, 5.946 mmol), copper iodide (113 mg, 0.595 mmol), tripotassium phosphate (6 .94 g, 32.703 mmol) and trans-1,2-dicyclohexanediamine (0.22 mL, 1.843 mmol) were added, dissolved in 1,4-dioxane, and then stirred at reflux for 12 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure, column purification (hexane: ethyl acetate = 8: 1 → hexane: methylene chloride = 2: 1) was performed, and the solution was distilled under reduced pressure to obtain a liquid wax 9- ( 6.39 g of 6-iodopyridin-2-yl) -9H-pyrido [2,3-b] indole was obtained (yield: 100%).

  (3) Synthesis of new host 1

  A new host 1 was synthesized according to the following reaction formula (3).

  9- (6-Iodopyridin-2-yl) -9H-pyrido [2,3-b] indole (2.39 g, 6.439 mmol), carbazole (1.08 g, 6.439 mmol) in a 250 mL 2-neck flask , Copper iodide (123 mg, 0.644 mmol), tripotassium phosphate (7.52 g, 35.41 mmol), trans-1,2-dicyclohexanediamine (0.24 mL, 1.996 mmol), and 1,4- After dissolving with dioxane, the mixture was stirred at reflux for 12 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure, column purification (hexane: methylene chloride = 3: 1 → 1: 1) was performed, the solution was distilled under reduced pressure and recrystallized with methylene chloride / petroleum ether solvent. 1.50 g of a white solid was obtained (yield rate: 81%).

  2. Synthesis of new host 2

  (1) Synthesis of 6-bromo-9- (6-iodopyridin-2-yl) -9H-pyrido [2,3-b] indole

  6-Bromo-9- (6-iodopyridin-2-yl) -9H-pyrido [2,3-b] indole was synthesized according to the following reaction formula (4).

  In a 250 mL two-necked flask, 2,6-diiodopyridine (6.96 g, 21.045 mmol), 3-bromo-carboline (2.60 g, 10.522 mmol), copper iodide (200 mg, 1.052 mmol), phosphoric acid Tripotassium (12.28 g, 57.871 mmol) and trans-1,2-dicyclohexanediamine (0.4 mL, 3.262 mmol) were added, dissolved in 1,4-dioxane, and stirred at reflux for 12 hours. I let you. After completion of the reaction, the solvent was removed by distillation under reduced pressure, column purification (hexane: methylene chloride = 3: 1 → 2: 1) was performed, and the solution was distilled under reduced pressure and recrystallized with methylene chloride / petroleum ether solvent. 1.37 g of a white solid was obtained (yield rate: 29%).

  (2) Synthesis of new host 2

  A new host 2 of phosphorescent compound was synthesized according to the following reaction formula (5).

  In a 250 mL 2-neck flask, 6-bromo-9- (6-iodopyridin-2-yl) -9H-pyrido [2,3-b] indole (1.37 g, 3.044 mmol), carbazole (1.02 g, 6.088 mmol), copper iodide (145 mg, 0.761 mmol), tripotassium phosphate (7.10 g, 33.484 mmol), trans-1,2-dicyclohexanediamine (0.3 mL, 2.131 mmol), After dissolving with 1,4-dioxane, the mixture was stirred at reflux for 12 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and then the column was purified with toluene to remove the color, and the column was purified (hexane: methylene chloride = 2: 1 → 1: 1), and the solution was distilled under reduced pressure. Then, recrystallization was performed with methylene chloride / petroleum ether solvent to obtain 0.40 g of a white solid (yield rate: 23%).

  The low-temperature PL (photoluminescence) spectra of the comparative host (ref. Host) represented by the following chemical formula (5) and the new host 1 and the new host 2 are shown in FIG. 2, and the comparative host (ref. Host) and the new host 1 The UV spectrum and PL spectrum of the new host 2 are shown in FIG. Table 1 shows the characteristics of the comparison host (ref. Host) and the new host 1 and the new host 2.

As shown in FIGS. 2, 3 and Table 1, the new host 1 and the new host 2 of the phosphorescent compound according to the present invention have a wide band gap energy of 3.3 eV or more and a triplet energy of 2.8 eV or more. (E _T ).

  That is, similar to the comparative host (ref. Host), it has a triplet energy higher than that of CBP used as the host material of the conventional light emitting material layer, and more than 2.8 eV of the triplet energy of a commonly used dopant. Since it is high, reverse energy transition from the dopant to the host can be prevented. In addition, since it has a wide energy band gap, it has an advantage of improving luminous efficiency.

  Furthermore, since the phosphorescent compound of the present invention has stronger electronic characteristics than the comparative host, the charge balance characteristics are improved and the light emission efficiency is improved.

  Hereinafter, the phosphorescent material according to the present invention and the organic light emitting diode using the phosphor will be described through comparative examples and experimental examples in which an organic light emitting diode element is manufactured using the comparative host and the phosphorescent compound of the present invention as a blue phosphorescent host, respectively. The device performance will be described in comparison.

<Comparative example>
An indium-tin-oxide (indium tin oxide: ITO) was deposited on the substrate to form an anode and washed. After the substrate on which the anode is formed is sent to a vacuum deposition chamber, a 50-thick hexaazatriphenylene-hexanitrile (HAT-CN) hole injection layer, a 550-thick 4,4′-bis [N -(1-naphthyl) -N-phenylamino] -biphenyl (NPB) hole transport layer, TAPC electron blocking layer with a thickness of 100 mm represented by the following chemical formula (6), represented by the above chemical formula (5) A light-emitting material layer having a thickness of 300 mm, in which a comparison host is doped with 15% of a blue dopant (FCNIr) represented by the following chemical formula (7), a TmPyPB electron transport layer having a thickness of 400 mm represented by the following chemical formula (8), A LiF electron injection layer having a thickness of 5 mm and an aluminum cathode having a thickness of 1100 mm were deposited.

<Experimental example>
An indium-tin-oxide (indium tin oxide: ITO) was deposited on the substrate to form an anode and washed. After the substrate on which the anode is formed is sent to a vacuum deposition chamber, a 50-thick hexaazatriphenylene-hexacarbonitrile (HAT-CN) hole injection layer, a 550-thick 4,4′-bis [ N- (1-naphthyl) -N-phenylamino] -biphenyl (NPB) hole transport layer, 100-inch thick TAPC electron blocking layer, and 15 new blue dopant (FCNIr) on new host 1 of formula (4) A light-emitting material layer having a thickness of 300 mm doped with%, a TmPyPB electron transport layer having a thickness of 400 mm, a LiF electron injection layer having a thickness of 5 mm and an aluminum cathode having a thickness of 1100 mm were deposited.

  The device characteristics of the comparative example and the experimental example are shown in Table 2 below, and graphs showing current density, current efficiency, and power efficiency are shown in FIGS. 4A to 4C.

  As shown in Table 2 and FIGS. 4A to 4C, the phosphor of the present invention has excellent characteristics such as current efficiency, power efficiency, and luminance. Therefore, the organic light emitting diode device using the phosphor of the present invention in the light emitting material layer has improved light emission efficiency and can reduce power consumption while realizing a high brightness image.

  An example of an organic light emitting diode element using the phosphorescent compound is shown in FIG.

  As shown in the drawing, the organic light emitting diode element is formed of a first and second substrate (not shown) facing each other, an organic formed between the first substrate (not shown) and the second substrate (not shown). Light emitting diode E.

  The organic light emitting diode E includes a first electrode 110 serving as an anode, a second electrode 130 serving as a cathode, and an organic light emitting layer 120 formed between the first electrode 110 and the second electrode 130. It consists of.

  The first electrode 110 is made of a material having a relatively high work function, for example, indium-tin-oxide (indium tin oxide: ITO), and the second electrode 130 is made of a material having a relatively low work function, for example, And aluminum (Al) or aluminum alloy (AlNd). In addition, the organic light emitting layer 120 includes red, green, and blue organic light emitting patterns.

  The organic light emitting layer 120 has a multilayer structure, that is, a hole injection layer (HTL) 121 and a hole transport layer (hole transport layer) sequentially from the first electrode 110 in order to maximize luminous efficiency. HIL) 122, an electron blocking layer 123, a light emitting material layer (EML) 124, an electron transport layer 125, and an electron injection layer 126. It consists of.

  The light emitting material layer 124 includes the phosphor of the present invention represented by the chemical formula (2).

  For example, when the phosphor layer 124 uses the phosphor of the present invention as a host material, a dopant can be added to emit blue light. Since the phosphor has higher triplet energy than the dopant, the reverse energy transition from the host material to the dopant can be prevented. Moreover, since it has a wide energy band gap, the light emission efficiency can be improved.

 Although the above has been described with reference to the preferred embodiments of the present invention, various modifications and alterations may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. It will be apparent to those skilled in the art that changes can be made.

 DESCRIPTION OF SYMBOLS 110 ... 1st electrode, 120 ... Organic light emitting layer, 121 ... Hole injection layer, 122 ... Hole transport layer, 123 ... Electron blocking layer, 124 ... Light emitting substance layer, 125 ... Electron transport layer, 126 ... Electron injection layer, 130 ... Second electrode

Claims (3)

Each of X and Y is independently selected from the group consisting of an aromatic compound and a heterocyclic compound ;
The phosphorescent compound , wherein X is substituted carbazole or unsubstituted carbazole, and Y is substituted carboline or unsubstituted carboline .

A first electrode;
A second electrode facing the first electrode;
A luminescent material layer positioned between the first electrode and the second electrode;
The light emitting material layer is represented by the following chemical formula, and each of X and Y includes a phosphorescent compound selected from the group consisting of an aromatic compound and a heterocyclic compound. Do Ri,
Said X is substituted carbazole or unsubstituted carbazole, and said Y is substituted carboline or unsubstituted carboline, The organic light emitting diode element characterized by the above-mentioned .

A hole injection layer positioned between the first electrode and the luminescent material layer; a hole transport layer positioned between the luminescent material layer and the hole injection layer; and the second electrode and the luminescent material layer. The organic light emitting diode device according to claim 2 , further comprising: an electron injection layer positioned between the light emitting material layer and an electron transport layer positioned between the light emitting material layer and the electron injection layer.

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